Morphological and experimental studies on the junctional complexes between Sertoli cells will be continued in an effort to understand the factors responsible for the establishment of the blood-testis barrier and those that control its transient opening to permit upward movement of preleptotene spermatocytes from the basal compartment into the adluminal compartment. Preliminary observation suggesting a local feedback mechanism between seminiferous tubules and the interstitial cells will be pursued further. There are indications that various pharmacological agents that suppress spermatogenesis result in a secondary stimulation of the Leydig cells in the immedate vicinity of the damaged tubules. This is a novel observation that deserves vigorous investigation. Studies of spermatogenesis by means of the freeze-fracturing techniques will be continued with the objective of following the internal differentiation of the various membranes in the acrosomal and post-acrosomal regions, and of clarifying the mechanisms of acrosome formation and head-shaping.